Metallurgical induction furnace



1937. J. c. HARRIS, JR 2,079,610

METALLURGICAL INDUCTION FURNACE Filed Nov. 20, 1954 2 Sheets-Sheet l y 1937- J. c. HARRIS, JR 2,079,610

METALLURGICAL INDUCTION FURNACE Filed Nov. 20. 1934 2 Sheets-Sheet 2 J Glfarrzb c/z' Patented May 11, 1937 UNITED STATES PATENT orrlcs 'IClaims.

This invention-relates to an electrical induction furnace of the type used for metallurgical purposes and, among other objects, aims to provide an improved induction furnace of the hori- 5- rontal ring type capable of operating at ordinary commercial frequencies and having provision for controlling the heat distribution in the charge or pool of metal according to the depth of the pool. Another feature of the invention is the provision of a relatively large hearth or charging chamber and communicating channels so constructed and arranged as to reduce pinch effect and the resulting tendency to rupture the metallie circuit in the channels.

15 Other aims and advantages of the invention will appear in the specification, when considered in connection with the accompanying drawings, wherein:

' Fig. 1 is a top plan view, more or less in out- 20 line, of a polyphase induction furnace embodying the invention;

Fig. 2 is a fragmentary sectional view taken on the line 22 in Fig. 1; and

Fig. 3 is a sectional view taken on the line 3-4 in Fig. 1. I

Referring particularly to the drawings, the induction furnace is shown as being of the polyphase, horizontal, open ring type, although it is to be understood that it may be single phase or two phase and one ormore transformer units may be employed. Herein, the furnace body I is composed of suitable refractory and insulating materials which are well known in the art and form no part of the present invention. In the refractory body there are provided three open channels I, which, in this instance, are shown as being substantially rectangular with rounded corners and each channel communicates with a central charging chamber or hearth l2 of substantial horizontal area. The cores I3 of three transformer units or phases are shown as projecting through vertical openings M in the refractory body and primary windings l5, shown in outline, are arranged on the vertical legs of the cores within said openings. In this example, the legs of the transformer cores are rectangular in cross section and the distance from the primary windlugs to the channels H is substantially uniform. Experience has demonstrated that the ring channels of induction furnaces have to be relatively small or of small cross sectional area to operate at the highest efliciency or with the highest power factor. However, in such furnaces, rupture of the secondary circuit is liable to occur, due to pinch effect in the molten metal or bath at irregular portions or narrow placesin the channels. Moreover, experience has shown that there must be a definite relationship between the size or sizes of the channels and of the charging chamber or hearth. If the hearth is made too large, the stray flux field therein will reduce the power factor. The problem of proper heat distribution in such furnaces is a very important consideration, and heretofore has not been properly solved. In accordance with this invention, the heat distribution throughout the poolof metal is controlled by the depth of the charge 2 above the, bottom of the hearth or charging chamber. This is accomplished by providing an elevated bottom for the hearth or chamber well 16 above the bottom level of the channels, as clearly shown in Fig. 3. The bottom of the hearth is shown in Figs. 1 and 3 as having inclined walls or portions 16 which merge with the bottom walls of the channels. Each of the bottom surfaces 20 may be treated as being a segment of the frustum of a cone. The idea is to avoid an abrupt reduction in cross section of the charge or pool at the mouths of the channels and in the magnetic flux paths leading into the central chamber. Since the channels are deeper than the hearth, the static pressure in their bottom portions for a given depth of the pool on the hearth, is greater than it would be if the hearth were lower. This increased static pressure tends to overcome the pinch eifect in the channels.

The size or horizontal area of the charging chamber or hearth is such that the cross section of the bath or pool in the path of the magnetic flux around each channel or ring may be increased or decreased to control the heat distribution. If the cross section of metal from the center of the chamber or hearth to one side wall is approximately equal to the cross section of the' metal in each channel, the resistance and, hence, 40 the temperature, will be nearly uniform throughout each of the secondary circuits, ignoring any heat that may be generated in or extracted from the pool by chemical reactions. If the cross section of the bath or pool in the chamber or hearth is decreased by lowering its level, the resistance and, hence, the temperature in the charging chamber, will be increased. If much heat of reaction is generated in the charging chamber, the temperature of the pool therein may be equalized with that in the channels by increasing the charge and the depth of the pool. This mode of controlling the heat distribution is important. If the temperature is kept nearly uniform throughout the pool, the refractory body of the furnace is relieved of destructive cracking strains which occur at hot or cold spots or areas due to unequal expansion and contraction. Another and very important advantage of making the chamber or hearth large and shallow, relative to the channels, resides in the fact that the metal in the pool is exposed to a greater slag surface which accelerates the chemical reaction between the metal and slag. If the furnace is used for refining metals or making alloys, this feature enables the operator to control the time required to produce the necessary reactions.

Referring to Figs. 1 and 2,.each of the channels ii is shown as being provided with dams in the form of refractory battles l1 near their mouths adapted to prevent slag in the charging chamber from entering and clogging up the channels. In this instance, the baiiles or dams are shown as being inserted in slots I8 and they are preferably, though not necessarily, adjustable vertically so that they will float on the surface of the molten metal. However, it is contemplated that they may be permanently secured in the refractory body at any desired height, especially if the furnace is to be used for a given purpose and the depth of the pool of molten metal is to be kept more or less constant. Moreover, it is contemplated that any suitable bailles may be employed to prevent the channels from becoming clogged with slag which is apt to freeze and cause trouble in them. As clearly shown in Fig. 2, the refractory dam I! is shown as resting on a molten charge of metal is in the channel I i. The depth of this pool of metal happens to be shown as being such as to produce substantially uniform heat distribution throughout the channels and the hearth or charging chamber.

Referring to Fig. 3, the furnace is shown as being provided with a tap opening. 20 extending through the bottom and it is adapted to be closed by a suitable plug 2| in the bottom of the hearth. However, it is to be understood that the tap opening may be provided at any convenient point. In this example, the bottom of the charging chamber or hearth is slightly dished or inclined toward the discharge opening so that all of the molten metal above the level of the hearth will run out by gravity. In some cases, it may be desirable to tap the molten metal from the channels, especially if the metal treated is a very expensive alloy or is of such characteristics as to crack the lining after the pool freezes. Obviomly, this may be done by tapping only one of the channels, or by tilting the whole furnace so as to partially or completely drain the channels.

To start the furnace in operation, ordinary starting rings may be introduced or suflicient molten metal may be charged to close the circuits through the chamber or hearth. It is also contemplated that pieces or scraps of metal may be charged into the chambers and channels and melted by means of ordinary electrodes (not shown) introduced into the charge to create a closed circuit and melt the pieces or scraps by the passage of current through them. The voltage of this starting circuit may be high enough to produce arcs between the contacting pieces of the charge in case the circuit is not closed between them. It will be understood by those skilled in the art that, suitable heat insulating covers (not shown) will be placed on the chamber and the channels to prevent excessive heat losses. In case the heat treatment is applied for any considerable length of time and the temperature is very high, as in the case of refining iron or steel and the treatment of other metals having relatively high melting points, the proper heat insulation becomes very important.

From the foregoing description, it will be seen that this invention provides a highly efficient induction furnace of a very simple design, which can be manufactured at a relatively small cost. It will operate very satisfactorily at high temperatures for melting, treating, refining or producing various metals and alloys. It is contemplated that the three phase design shown will be quite satisfactory from the commercial standpoint. However, it is distinctly understood that the design here shown is to be treated as being illustrative only and that the invention is capable of many embodiments.

Obviously, the present invention is not restricted to the particular embodiment thereof herein shown and described. Moreover. it is not indispensable that all the features of the invention be used conjointly, since they may be employed advantageously in various combinations and sub-combinations.

What is claimed is:

1. In an electric furnace of the horizontal open ring and core type, a hearth having its entire bottom elevated above the bottom of the ring channel and of greater width than that of the channel to provide a charging space, and a melting and refining pool.

2. In an electric induction furnace of the horizontal, open ring and coretype, a relatively wide hearth having its entire bottom elevated above the level of the bottom of the ring channel, the difference in elevation being such as to create a static pressure of molten charge in the channel tending to overcome the pinch effect in the channel and to control the heat distribution throughout the charge.

3. In a polyphase induction furnace of the horizontal ring and core type, a central charging chamber; and a plurality of channels deeper than any part of the charging chamber and communicating therewith, the bottom of the chamber having inclined portions leading to the bottoms of the channels at their mouths to avoid any abrupt reduction in vertical cross sectional area of the molten charge at the mouths of the channels.

'4. In a polyphase induction furnace of the horizontal ring and core type, a central charging chamber; symmetrically arranged and generally I rectangular channels of greater depth than any part of the chamber and communicating therewith.

5. In a polyphase, electrical induction furnace of the horizontal ring and core type, a central charging chamber; ring channels of greater depth than any part of the charging chamber communicating therewith; said chamber having a dished bottom wall and a metal outlet leading therefrom.

6. That mode of controlling the temperature distribution within any desired range in an induction furnace of the horizontal ring type and having a charging chamber, which consists in varying the cross section of the bath in the chamber relative to the cross section of the bath in the ring channel according to the total volume of the bath, whereby the temperature throughout the ring and chamber may be maintained substantially constant at high temperatures to prevent excessive cracking strains due to expansion and contraction.

7. That mode of controlling the temperature distribution within a desired range in an induction furnace, which consists in varying the cross section of a. portion of the secondary circuit by changing the depth of the molten bath so that the temperature in said portion may be higher than, equal to or less than that in any other portion of the secondary.

JAMES C. HARRIS, JR. 

